Abstract: A method and a device for reducing speckle formation on a projection display when working with a coherent light source. In this context, the light coming from the light source, before the projection, may strike an electrically controllable optical element having a spatially inhomogeneous refractive index, passing through the same, the refractive index being varied over time within the projection period. This may lead to an averaging out of the speckle pattern on the projection screen. For purposes of illumination, a multimode light source may be used, and/or the light coming from the light source is separated into a plurality of spatial modes, thereby reinforcing the effect. As an optical element, one may employ a liquid crystal element composed of at least two liquid crystal layers, to which a spatially dependent voltage is applied to generate a spatially dependent refractive index. Its birefringence may be compensated by orientating the layers to one another in appropriate fashion.

Abstract: A device for generating, adding and subtracting digital sequences of optical pulses and a method for the secure transmission of information. An interferometer having at least one electro-optical switch or electro-optical modulator positioned in one of its branch sections is used so that binary optical pulse sequences may be added and/or subtracted in the context of an electro-optical device and a method for the secure transmission of information using optical signals.

Abstract: A method and system for the secure transmission of messages between at least two users of a telecommunications network, using a secret, random binary encryption key, which is used once for encryption. The key is generated in a key generator recorded on at least two portable data media, such as CDs, and then output in this form to the users, each of whom receives one data medium containing the recorded key. The key is not stored in any other location. The users insert the recorded key media into reading devices, which are respectively assigned to telecommunications equipment, e.g., telephones, fax machines, or PCs, employed by the users. When a connection is established, logistics devices, which are also assigned to the telecommunications equipment, check whether the keys were entered properly and whether they correspond to each other. The logistics devices also synchronize the entered keys, or at least portions of the keys, when the information to be transmitted is encrypted and decrypted.

Abstract: A method and arrangement for generating binary sequences of random numbers uses the principle of random selection of the path of photons on a beam splitter and generating a random number by using two detectors (D10, D21) downstream from a beam splitter (ST2). To generate photons, a light source (L) of a low power is used, and an additional beam splitter (ST1) is connected upstream from the beam splitter (ST2). The photons emitted by the light source (L) during a predefined measurement time are split by the beam splitters (ST1, ST2) arranged one after the other in the beam path of the light source (L). The random sequence is generated when the splitting of the photons matches a predefined photon scheme.

Abstract: To provide a phase modulator for introducing a topological phase, which is designed to produce any desired phase shift between zero and 360°, the phase modulator has means, at least one double-refractive, electrooptical delay element having a rotatable indicatrix, which is/are used to direct the polarization of the light, during transmission through the modulator, over at the light one closed path on the Poincaré sphere, the indicatrix rotating in accordance with the predefined phase shift, and the total encircled surface on Poincaré sphere being equal in terms of absolute value to ?.

Abstract: The present invention provides an optical communications link having at least one optical fiber, in particular for communications transmission, where the optical fiber is repeatedly bent. The fiber sections having a right-hand and left-hand curvature are distributed in such a way over the communications link that the average torsion of the fiber is approximately zero. The communications link in accordance with the present invention is compact, flexible, and variable in length. In addition, it reduces the sensitivity of the polarization state of the optical signal to changes in the form of the communications link.

Abstract: The present invention is directed to a sensor for detecting changes in the distance between a first and a second location, having at, least one substantially helically coiled optical fiber, which is able to be mechanically connected to at least one of the locations, and having a light transmitter and a detecting device for optical signals, the detecting device being able to generate an output signal, which is dependent upon the polarization state of the optical signal transmitted via the optical fiber.

Abstract: A method and an apparatus for generating a random number on a quantum-mechanics machanics basis using the fundamentally random choice of path of a quantum particle on a beam splitter. Detectors are provided for capturing the particles being assigned to the outputs of the beam splitter. The detectors or their counting events represent different number values of the random number, or random number sequence. The generation of a multi-particle state in the output channel of the beam splitter, and thus of several particles which impact on a detector (D1, D1′, D2, D2′), significantly and advantageously increases the response probability of the detector and thus the probability of obtaining a useable counting event for every multi-particle state generated by the particle source. In this way a random sequence can be obtained more rapidly and more reliably than with single-particle detection.

Abstract: In order for binary optical pulse sequences to be able to be added and/or subtracted in the context of an electro-optical device and a method for the secure transmission of information using optical signals, an interferometer is used, which has at least one electro-optical switch or modulator positioned in one of its branch sections.

Abstract: A method and device for generating a choice of individual photons or photon pairs in an optical channel. The generation of this choice involves generating a two-photon state corresponding to a photon pair and spatially separating the photon pair while preserving the quantum-mechanical correlation, in the event the photons are emitted in a collinear manner. One photon is coupled into one optical channel each, the one channel containing an interferometer with variable optical path-length difference &dgr;1F−&dgr;1S, and the other channel including an optical delay section having the optical length &dgr;1.